1. Field of the Invention
The present invention relates to an electronic device such as a transmitter receiver unit which is used for a portable telephone, or the like.
2. Description of the Related Art
A conventional electronic device will be described with reference to FIG. 6 through FIG. 8, in which FIG. 6 is a perspective view of the conventional electronic device, FIG. 7 is an exploded perspective view of a part of the same, and FIG. 8 is a sectional view of a major part of the same.
In these drawings, a case 41 formed of a plastic material contains a bottom wall 41a, four side walls 41b, an opening 41c that is open upward facing to the bottom wall 41a, a large through-hole 41d formed on the bottom wall 41a, a through-hole 41e for taking out cables, L-letter shaped pawls 41f provided on several points around the large through-hole 41d, which have recesses facing the large through-hole 41d, ears 41g flush with the bottom wall 41a, provided on the corners outside the side walls 41b, through-holes 41h formed on the centers of the ears 41g, projections 41k projected inward on the side walls 41b, female screws 41m provided on the centers of the projections 41k, a metal film 41n overlaid on all the surfaces of the case 41 by plating or the like.
A rectangular thermal conduction member 42 made of a metal plate comprises a flat portion 42a, tongue pieces 42d cut and raised upward by cutting out parts of the flat portion 42a, and a plurality of through-holes 43 provided on the flat portion 42a.
The thermal conduction member 42 is housed inside the case 41 with the cut and raised tongue pieces 42d directing upward, and is attached to the case 41 by hooking the periphery of the flat portion 42a inside the L-letter shaped pawls 41f, so that the flat portion 42a closes the large through-hole 41d of the case 41.
There are a vertical difference of dimension between the height (inner dimension) of the recess of the pawl 41f and the thickness of the thermal conduction member 42, and a lateral difference of dimension between the two pawls 41f facing each other across the large through-hole 41d and the width of the thermal conduction member 42. Accordingly, the thermal conduction member 42 has plays against the case 41 in the vertical and lateral directions.
A printed circuit board 44 contains through-holes 48 and conductive patterns (not illustrated). The printed circuit board 44 has a connector 45 for connecting a cable and heating components 46 with higher calorific values, etc., mounted on a lower side 44a thereof, and electronic components 47 with lower calorific values, etc., mounted on a upper side 44b.
A box-shaped metal cover 49 made of a metal plate has the lower side opened, and a plurality of through-holes 50 on the upper side. This metal cover 49 is attached to the printed circuit board 44 so as to overlay the electronic components 47 on the upper side 44b, which electrically shields the electronic components 47 mounted on the upper side 44b.
The printed circuit board 44 is mounted on the case 41 in such a manner that the lower side 44a with the heating components 46 mounted thereon faces the bottom wall 41a of the case 41 to close the opening 41c, and is attached to the case 41 by screwing male screws 51 put through the through-holes 48 of the printed circuit board 44 into the female screws 41m provided on the projections 41k of the case 41.
In a state that the printed circuit board 44 is attached to the case 41, the thermal conduction member 42 faces to an area including the heating components 46 on the lower side 44a of the printed circuit board 44, and the tongues 42d of the thermal conduction member 42 are in contact with the surfaces of the heating components 46 mounted on the lower side 44a of the printed circuit board 44.
The case 41 with the printed circuit board 44 and the thermal conduction member 42 attached thereon is mounted on the surface of a mother board 52 where conductive patterns 52a are formed, and it is fastened to the mother board 52 by screwing male screws 53 put through the through-holes 41h formed on the ears 41g of the case 41 into female screws 52b made on the mother board 52.
In the electronic device having the aforementioned construction, the heat generated by the heating components 46 diffuses into the whole thermal conductive member 42 through the tongue pieces 42d being in contact with the surface of the heating components 46, and radiates from the thermal conduction member 42.
However, in the conventional electronic device, since the thermal conduction member 42 is attached to be hooked by the pawls 41f of the case 41, there is play between the pawls 41f and the thermal conduction member 42. Accordingly, the electronic device emits play noises due to vibrations of the thermal conduction member 42 when receiving vibrations and impacts from outside, or breaks the heating components 46 by the friction between the tongue pieces 42d and the surface of the heating components 46, which is a problem.